This invention relates to electrodes, and more particularly, to electrodes useful in voltaic cells and batteries utilizing halogens such as bromine, chlorine, and iodine and metals such as zinc and cadmium as their electrochemically active agents.
Voltaic cells which include an aqueous solution of zinc halide or cadmium halide as the electrolyte are known. These devices are characterized by relatively high self-discharge rates, low capacities, and high internal resistances. Since liquid halogen is soluble in the aqueous electrolyte, it is difficult to keep metallic zinc or cadmium and liquid halogen apart while simultaneously achieving a system in which a good percentage of the theoretical energy storage capacity can be realized.
Various attempts have been made to prevent elemental halogen from migrating to the zinc or cadmium electrode. For example, U.S. Pat. No. 3,352,720 to G. R. Wilson et al. teaches the use of electrolyte insoluble polymeric amine halogen complexes in place of the elemental halogen. This cell suffers from a low capacity and a high self-discharge rate because of the low stability of the polyhalogens employed and because the solid complexes are distant from the inert current collector and therefore are not readily available for electrochemical reaction.
U.S. Pat. No. 3,816,177 to Myles A. Walsh teaches the use of soluble quaternary ammonium halides dissolved in the electrolyte in combination with a water soluble complexing solvent which combines with the quaternary polyhalides formed during liberation of liquid halogen to form insoluble, halogen rich, oil-like complexes. If an inert electrode made of a material which absorbs the complex is employed, an improved cell is provided, since the complex is relatively stable and since the halogen molecules, being concentrated about the current collector, are available for electrochemical reaction to an improved degree. The present invention, however, represents a further improvement in such halogen cells and batteries.